The present document is based on Japanese Priority Document JP 2001-002853, filed in the Japanese Patent Office on Jan. 10, 2001, the entire contents of which being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a transformer apparatus suitable for use as a converter transformer of a switching power supply and the like.
2. Description of the Related Art
In a converter transformer of a switching power supply, the number of turns of a primary coil and the number of turns of a secondary coil are set at a predetermined turn ratio, and thereby the converter transformer is structured to obtain a predetermined output voltage in response to an input voltage on the basis of the turn ratio. In the converter transformer, the improvement of the efficiency of the switching control circuit thereof is achieved by the setting of the switching frequency thereof to be a higher frequency, and the miniaturization of the transformer itself and the switching control circuit is achieved by the decrease of the inductance thereof.
In the converter transformer, the number of turns on the primary coil side has been decreased as a measure of the increase of the switching frequency. In the converter transformer, if, for example, the number of turns on the secondary coil side is wanted to be set at under 0.5 turn in relation to the turn ratio between the primary coil and the secondary coil to be set, its realization has been difficult owing to the configuration of the core of the converter transformer. In other words, in conventional converter transformers, the lower limit of the number of turns on the primary coil side is determined by the limit of the number of turns on the secondary coil side. Consequently, there has been a problem that the merits of the increase of the switching frequency mentioned above cannot be fully effective.
For the resolution of the aforesaid problem, Japanese Patent Publication No. 2,751,284 discloses a transformer having a core member constituting a magnetic path, which includes a first and a second magnetic leg portions that have a first and a second sectional areas and are provided with a first and a second windings, respectively, and a secondary coil constituted with the first and the second windings connected in parallel to each other to form a secondary coil. Because the thus disclosed transformer enables the selection of the turn ratio between the primary coil and the secondary coil besides the ratios of integers, it becomes possible to obtain a desired output voltage at a small voltage regulation.
Now, the aforesaid disclosed transformer has a structure in which coil wires are wound on each magnetic leg portion by predetermined numbers of turns, respectively. The disclosed transformer is small in its whole size owing to such a structure, and consequently has a problem that, when each magnetic leg portion is small the winding treatment of a coil wire to each magnetic leg portion is troublesome to make production efficiency thereof worse. The disclosed transformer also has problems such as breaking of a coil wire to be wound on each magnetic leg portion and limitation of the amount of electric current to be supplied.
Accordingly, the present invention is proposed with an object to provide a transformer apparatus including a secondary coil having a small number of turns, which enables improvement of in productivity thereof.
A transformer apparatus according to the present invention, which achieves the aforesaid object, comprises a core member, a primary coil, and a secondary coil composed of a first and a second plate coil members and a plurality of connecting coil pieces. The core member is composed of a base portion, a center core portion fixed at a center part of a principal plane (major plane) of the base portion to stand to be one body with the base portion, and at least three side core portions situated at regular intervals from each other around the center core portion in peripheral parts on the principal plane of the base portion and fixed to stand to be one body with the base portion. The primary coil is disposed at an outer periphery portion of the center core portion of the core member. The first plate coil member is formed in a basic shape of a frame-like body having side portions surrounding the outside of each side core portion respectively. The second plate coil member is also formed in the basic shape of a frame-like body having side portions surrounding the outside of each side core portion respectively, and the second plate coil member is combined with the first plate coil member with an insulating layer put between them in a laminated state. The connecting coil pieces are provided correspondingly to each side core portion of the core member in a condition of being respectively cantilevered by each side portion of the second plate coil member, and each free end of the connecting coil pieces extends to surround the outer periphery portion of each corresponding side core portion and further extends to be opposed to each adjoining side portion to be connected with the first plate coil member.
In the thus configured transformer apparatus according to the present invention, the first plate coil member and the second plate coil member are combined having the insulating layer put between them in the laminated state on the core member. In the transformer apparatus, each connecting coil piece having one end portion fixed to the second plate coil member surrounds the outer periphery portion of each side core portion, and the free end of each connecting coil piece is connected with the first plate coil member. In the transformer apparatus, the first plate coil member, a connecting coil piece and the second plate coil member constitute a unit secondary coil corresponding to each side core portion, respectively. In the transformer apparatus, by appropriate connection of each unit secondary coil, a secondary coil having the number of turns other than integers is configured as a whole. Consequently, in the transformer apparatus, the number of turns on the secondary coil side can be set bit by bit by a simple process of incorporating the first plate coil member and the second plate coil member on the core member, and then the output voltage thereof can be set in a large span.
As described above in detail, according to a transformer apparatus of the present invention, a frame-like shaped plate coil member having an n-gon shape is combined with a core member having n-pieces of side core portions in a laminated state, and opposed each side portion is connected with a connecting coil piece. Thereby, a secondary coil composed of a unit secondary coil of 1/n turn is configured. Consequently, it becomes possible to set the turn ratio of the primary coil and the secondary coil little by little, and to set the turn ratio at a value besides integer ratios. Then, the output voltage of the transformer apparatus can be set within a wide range. Consequently, the transformer apparatus can easily deal with the increase of the switching frequency, and can improve the efficiency of the switching control circuit thereof. Moreover, it can be achieved that the transformer itself and the switching control circuit are miniaturized owing to the decrease of the inductance thereof.
Furthermore, the transformer apparatus is small in size as a whole, for example, and requires no troublesome winding treatment of respective coil wires on small side core portions. Consequently, the assembling thereof becomes simple and easy, which can achieve the improvement of the productivity thereof greatly. Because the transformer apparatus is equipped with coils as plate coil members, the generation of the disadvantage of the breaking of a coil wire can be decreased, and the limitation of the amount of electric currents is relieved. Moreover, the efficiency of heat dissipation becomes higher and the degree of precision can also be heightened greatly.